TM4SF19 and rheumatoid arthritis: In our previous study, we demonstrated that Tm4sf19 regulates osteoclast differentiation by interacting with integrin αv, and LEL-Fc suppressed the osteoclastogenesis by inhibiting their interaction.22 The expression of integrin αvβ3 was increased in RA synovium compared to healthy controls, and integrin αvβ3 was highly expressed in synovial fibroblasts involved in cell migration, adhesion, and invasion.